Development of Acceleration Grid Power Supply of NNBI System for CRAFT

Acceleration grid power supply (AGPS) is the energy provider of the negative neutral beam injection (NNBI) system. With the construction of the Comprehensive Research Facility for Fusion Technology (CRAFT), higher parameter requirements are proposed and a high-voltage power supply (HVPS) rated
$-200\sim -400$
kV/28 A has been developed. This article introduces the design of each part of the AGPS in detail, such as the neutral-point-clamped (NPC) inverter, step-up transformer, and diode rectifier. The control system is also discussed and an optimized mathematical model from the duty cycle of the inverter to the dc output of the power supply (PS) is given. A scheme is put forward to solve the special grid breakdown (GB) condition of NNBI AGPS. The experimental results demonstrate that AGPS can meet the rated output requirements of the NNBI system and it can be quickly turned off to protect the AGPS in GB condition, which provides a related reference for the subsequent development of other HVPS for auxiliary heating of nuclear fusion.